In the list of connected devices you see all the devices and clients you
generated a device password for and their last activity:

You can use the trash icon to disconnect any of the devices in the list.

At the bottom of the list you find a button to create a new device-specific
password. You can choose a name to identify the token later. The generated
password is used for configuring the new client. Ideally, generate individual
tokens for every device you connect to your account, so you can disconnect
those individually if necessary.

Note

You have only access to the device password when creating it,
Nextcloud will not save the plain password, hence it’s recommended to
enter the password on the new client immediately.

Note

If you are Using two-factor authentication for your account,
device-specific passwords are the only way to configure clients. The
client will deny connections of clients using your login password then.